1. Field of the Invention
The present disclosure relates to a photoelectric conversion device, an image pickup system, and a driving method of photoelectric conversion device.
2. Description of the Related Art
In a field of image pickup apparatuses, switching of gains may be performed for the same signal in a sequential manner. Japanese Patent Laid-Open No. 2010-016416 describes an image pickup system in which each of amplifiers provided for respective columns of a pixel array amplify a single signal with different gains, each of the amplifiers corresponding to a corresponding one of the columns, and which widens a dynamic range by selecting and using one of resulting signals in accordance with the signal level. As a method for amplifying a signal with different gains, Japanese Patent Laid-Open No. 2010-016416 describes a method in which switching of gains is performed in a single amplifier and processing is performed in a sequential manner.
However, in Japanese Patent Laid-Open No. 2010-016416, an operational amplifier, which includes an active element, is used as an amplifier. Thus, in a method in which switching of gains is performed in an amplifier in a sequential manner, a settling time for an output of the amplifier to settle depends on the responsivity of the operational amplifier. Consequently, every time a switching of gains is performed, a settling time is needed. Therefore, the operation speed of an image pickup device is limited by the responsivity of the operational amplifier.